Fig. 3

Decreased capillary-to-fiber ratio and thicker capillary basement membranes in patients with PCS. Example of a semithin transverse section of a vastus lateralis muscle biopsy specimen stained with toluidine blue, displaying capillaries and muscle fibers, and quantification of C/F, MCSFA and capillary density (A). Representative electron micrographs of transverse ultra-thin sections of muscle capillaries (B). Orange lines indicate typical sites of measurements for the capillary basement membrane thickness. The large graphs depicts all 3732 individual measurements except 35 outliers with values above 350 µm. Coloured dotted lines indicate the respective group means. Small graphs indicate subjective scoring of capillary pathology as well as mean CBM thickness values per individual samples. Schematic cross-sectional representation of a capillary (created with BioRender.com) with results of TBIA morphometric analysis (C). Exemplary micrographs of transverse ultra-thin sections of damaged muscular capillaries from PCS-4 (D). Immunohistochemical expression of CD169/SIGLEC1 in the biopsy specimen obtained from PCS-4 (E). 400 × magnification, black scale bar = 100 µm. Ordinary one-way ANOVA with Tukey's multiple comparisons test. * = p < 0.05, ** = p < 0.005, *** = p < 0,0005. C/F capillary-to-fiber ratio, MCSFA Mean cross-sectional fiber area, CBM Capillary basement membrane, EC Endothelial cell, TBIA Tablet-based image analysis